Mysterious Sea Creatures in Australia Chew Up Teenager’s Legs

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Sam Kanizay, 16, being treated at a hospital in Melbourne, Australia. Doctors and scientists said they were baffled by the severity of the injury, which was sustained at a beach.CreditCreditJarrod Kanizay, via Australian Associated Press

SYDNEY, Australia — Australians tend to roll their eyes when the world obsesses about this country’s dangerous animal kingdom, including its deadly snakes (the deadliest in the world), its tiny and toxic redback spiders, and of course the jellyfish that cause heart attacks.

But on Monday, even the most jaded Aussies found themselves gawking over and swearing about the mysterious creatures that chewed up a Melbourne teenager’s legs.

Graphic photos of his ankles spread across social media.

yikes! Australian teen comes out of the ocean pouring blood. attacked by some tiny creatures. maybe sea lice?? https://t.co/VcF4DGPMha

All that the teenager, Sam Kanizay, 16, said he had wanted to do was soak his sore legs at Dendy Street Beach in Brighton after a football match. But when he stepped out of the water a half-hour later, his ankles were pouring blood.

Doctors and scientists said they were baffled by the severity of the injury.

The leading theory seemed to be that Sam had inadvertently become lunch for hungry sea lice, also known as marine isopods, a group of crustaceans that are the marine versions of slaters and pill bugs that people might be familiar with from their gardens. Sea lice are usually parasites of fish. When they bite humans, they usually just leave tiny pinpricks that can look like a rash.

Sam’s father, Jarrod Kanizay, decided to investigate by dropping a hunk of raw steak in the water where his son was attacked. He posted a video of the result: hundreds of tiny sea creatures feasting on the meat.

But not everyone is convinced that the true culprit has been caught.

A University of New South Wales associate professor, Alistair Poore, said the animals in the video were not sea lice, but another group of small scavengers called amphipods, which are not known to bite humans.

“You can attract a lot of animals in the sea with raw meat,” Dr. Poore said. “Even though it’s interesting, it doesn’t prove to me they were the ones that bit his legs.”

Dr. Poore said he was doubtful that this was a particularly aggressive strain of sea lice but suspected that there may be greater numbers in the area than normal — something that may be caused if a lot of dead fish were in the area.

Although a similar sea lice attack on another teenage boy was reported at a nearby beach in 2015, Dr. Poore said sea lice lived all over the world: “It’s not an Australian thing.”

“It’s a fascinating story to show that the animals are out in urban areas, we don’t live totally separated from nature,” Dr. Poore said. “Just like there are mosquitoes and leeches on land that will bite humans, the same happens in the ocean.”

Damien Cave regrets his new seaside rental. Tacey Rychter is waiting for the inevitable horror movie “Attack of the Isopods” to come out.

A version of this article appears in print on , on Page A7 of the New York edition with the headline: What Bloodied an Australian Teenager’s Feet? An Undersea Mystery Captures Global Interest. Order Reprints | Today’s Paper | Subscribe